The present invention relates to a bucket tooth which is attached to a bucket of construction equipment or the like and is used mainly for a work of excavating or loading earth and sand and a method of manufacturing the bucket tooth.
Hitherto, the most common bucket tooth used for construction equipment or the like is of a type in which the bucket tooth is fit in an adapter fixedly provided on a bucket side and is fastened by a pin or the like. A bucket tooth of a type which is directly fastened to a bucket by using a bolt is also known.
FIGS. 23(a1) and 23(a2) through FIGS. 23(d1) and 23(d2) show examples of the bucket tooth of the latter type. In each of bucket teeth 50A, 50B, 50C, and 50D, the tip side opposite to a base portion having a plurality of bolt holes 51 is formed with a step, or the base portion is formed in a forked shape. The inner portion of the step or the inner space of the forked portion is placed in contact with the tip of a bucket lip (not shown) and the bucket tooth is fixed to the bucket lip by being bolted.
Another example of the bucket tooth of the bolting type is, as shown in FIGS. 24(a) and 24(b), a bucket tooth 60 of a shape having edges 61 at both one end and the other end and two bolt holes 62, 62 in the center. The bucket tooth 60 can be used twice in such a manner that when the edge 61 at one end is worn and becomes short to the limit, the bucket tooth 60 is turned and the edge 61 at the other end is used.
In the conventional bucket teeth shown in FIGS. 23(a1) and 23(a2) through 23(d1) and 23(d2), however, when the tip of each of the tooth becomes useless by wear, the bucket teeth 50A to 50D have to be replaced by new bucket teeth. Consequently, there is a problem such that the life is relatively short due to the wear, and since the weight of the worn portion with respect to the weight of the whole tooth is small, the yield is low.
On the contrary, in the conventional bucket tooth shown in FIGS. 24(a) and 24(b), even when one of the edges 61 is worn out, the tooth is turned and the other edge 61 can be used. Consequently, it has advantages such that the life is relatively longer in spite of the wear and the yield is higher as compared with the bucket teeth shown in FIGS. 23(a1) and 23(a2) through FIGS. 23(d1) and 23(d2). On the other hand, the bucket tooth has a problem which is common to bucket teeth of the bolting type, such that a fastening bolt is easily loosened due to vibration, shock, and the like applied to the bucket tooth during operation.
The present invention is achieved in order to solve such problems. An object of the present invention is to provide a bucket tooth to be attached by being fastened by a bolt which is prevented from being loosened during operation, and to provide a method of manufacturing the bucket tooth, which can prevent a bolt from being loosened.
In consideration that a direct cause of loosening of a fastening bolt attaching a bucket tooth to a bucket lip is reduction in axial force of the bolt during operation, the present invention has been achieved by finding out effective means which prevents the reduction in axial force.
According to a first aspect of the present invention, there is provided a bucket tooth attached to a bucket lip via a fastening bolt, comprising axial force fluctuation absorbing means for absorbing fluctuations in axial force of the fastening bolt after attaching the bucket tooth to the bucket lip.
In the present invention, preferably, after the bucket tooth is attached to the bucket lip, fluctuations in axial force of the fastening bolt are absorbed by the axial force fluctuation absorbing means. Even when fluctuations in axial force occur in the fastening bolt in association with fluctuations in a load applied to the bucket tooth during operation, the fluctuations in axial force can be absorbed, thereby enabling reduction in axial force of the fastening bolt to be prevented. Obviously, according to the bucket tooth of the present invention, by providing a bolt fastening portion in the center portion, when the tip of the tooth becomes useless due to wear, the bucket tooth is turned and the other tip of the tooth can be used. Therefore, the bucket tooth having the increased life in spite of the wear and the improved yield can be achieved.
In the present invention, preferably, the axial force fluctuation absorbing means allows the bucket tooth to generate a resilient return force by causing a warp by resilient deformation so that one face side becomes a concave face and performing bolting in a state where the one face side is positioned on the bucket lip side. In such a manner, the fastening force at the time of bolting works as an action force in the direction of canceling the warp caused in the bucket tooth, the resilient return force is generated in the bucket tooth by the action force, the fluctuations in axial force of the fastening bolt during operation are absorbed by the resilient return force, and the reduction in axial force can be prevented.
In the present invention, preferably, the warp created in the bucket tooth is caused around a bolt hole into which the fastening bolt is inserted as a center, and an amount s of the warp is set to a value satisfying an equation of 2 mm/mxe2x89xa6sxe2x89xa615 mm/m. Specifically, when the amount s of the warp increases, an effect of preventing the reduction in axial force of the fastening bolt can be obtained. A value equal to or lower than 10% is obtained as an axial force reduction rate which does not cause any problem in practice in the case where the amount s of the warp is set to 2 mm/m or larger. When the amount s of the warp exceeds 15 mm/m, it is not preferable since an excessive tensile stress works around the bolt hole at the time of bolting and it causes delayed fracture.
In the present invention, preferably, the axial force fluctuation absorbing means allows the bucket tooth to generate a resilient return force by spot facing the circumference on the side facing the bucket lip, of a bolt hole in which the fastening bolt is inserted. In such a manner, the spot facing portion around the bolt is resilient deformed in the direction so as to be in contact with the bucket lip by the fastening force at the time of bolting, thereby generating the resilient return force in the spot facing portion. By the resilient return force, the fluctuations in axial force of the fastening bolt during operation are absorbed and the reduction in axial force can be prevented. The present invention is effective even when the bolt hole is not in the center portion of the bucket tooth. When one side of the bucket tooth of a type in which the bolt hole is in the center portion is worn, the bucket tooth is turned and the other side is used.
In the present invention, preferably, the axial force fluctuation absorbing means allows the bucket tooth to generate a resilient return force by causing a warp by resilient deformation so that one face side becomes a concave face, spot-facing the circumference on the side facing the bucket lip, of a bolt hole in which the fastening bolt is inserted, and performing bolting in a state where the one face side is positioned on a bucket lip side. By warping the bucket tooth and forming the spot facing portion around the bolt hole in such a manner, by a synergistic effect of them, a larger resilient return force can be generated and the effect of absorbing the fluctuations in axial force of the fastening bolt can be increased.
Preferably, a ratio (z) of a depth L of the spot facing to a diameter D of the spot facing (=L/D) is set to a value satisfying an equation of 2 mm/mxe2x89xa6zxe2x89xa618 mm/m. More specifically, when the spot facing amount (z) is increased, an effect of preventing the reduction in axial force of the fastening bolt can be obtained. However, a value equal to or lower than 10% is obtained as an axial force reduction rate which does not cause any problem in practice in the case where the spot facing amount (z) is set to 2 mm/m or larger. When the spot facing amount (z) exceeds 18 mm/m, it is not preferable since an excessive tensile stress works around the bolt hole at the time of bolting and it causes delayed fracture.
According to another aspect of the present invention, there is provided a bucket tooth attached to a bucket lip via a fastening bolt, wherein a bearing surface of the fastening bolt is formed in a tapered surface which is tapered down in an insertion direction of the fastening bolt.
In the present invention, the bearing surface of the bolt for fastening the bucket tooth can be set in the direction so as to cross the direction of a load (excavating force) acting on the bucket tooth at the time of excavation, preferably, in the direction almost perpendicular to the direction of the load. Consequently, the area for holding the axial force of the bolt increases, and the force acting on the bucket tooth can be received by the bolt bearing surface most effectively, in other words, uniformly. A local fatigue is not accordingly easily caused on the bearing surface, so that the reduction in axial force of the bolt can be prevented. As a result, the bolt can be certainly prevented from being loosened.
In the present invention, the angle of the tapered surface is preferably set within a range from 20xc2x0 to 45xc2x0 with respect to a center line of a bolt hole. When the angle of the tapered surface (bearing surface angle) is too large or too small, a shear component of an excavating force (load) acts on the bearing surface. Each time the load acts, a slight sliding occurs in the bearing surface and it causes increase in fatigue. When the bearing surface angle is particularly too small, the height of the head of the bolt is regulated by the thickness of the bucket tooth, the diameter of the bearing surface is reduced, and it causes a reduction in axial force. The relation between the bearing surface angle and the axial force reduction rate has been examined and found that, when the bearing surface angle is set within the range from 20xc2x0 to 45xc2x0, the axial force reduction rate can be set within the allowable range. More preferable, the bearing surface angle is set to 30xc2x0.
According to another aspect of the present invention, there is provided a bucket tooth attached to a bucket lip via a fastening bolt, wherein a bearing surface of the fastening bolt is formed in a spherical curved surface which is tapered down in an insertion direction of the fastening bolt.
In the present invention, the load (excavating force) acting on the bucket tooth at the time of excavation can be directed almost perpendicular to a tangent direction of the bolt bearing surface. The load can be therefore received by the whole bolt bearing surface. Accordingly, a local fatigue does not easily occur on the bearing surface. The reduction in axial force of the bolt can be prevented and the bolt can be certainly prevented from being loosened.
According to further another aspect of the present invention, there is provided a bolted structure of any of the above bucket teeth, wherein either the bucket lip or bucket tooth is tapped, and the bucket lip and the bucket tooth are fastened to each other by a fastening bolt inserted from the other side. In such a manner, the length of the screw portion can be increased, and an effect such that the bolt is not easily loosened is therefore produced. Since the load is supported only by the bolt head, the number of fatigued portions in the bearing surface, which cause reduction in axial force is reduced. The bolt is accordingly prevented from being easily loosened.
In the present invention, there is provided a bolted structure of any of the above bucket teeth, wherein the bucket lip and the bucket tooth are fastened to each other by screwing the tip of a fastening bolt inserted from either the bucket lip or the bucket tooth into a nut on the other side. In such a manner, even though the center line of a hole through which a bolt is inserted is deviated, no application of a load on one side due to the axial deviation occurs, so that the bolt is not easily loosened. Since the length of the core of the bolt can be increased, the repetitive load acting on the bolt can be reduced. There is an advantage such that the bolt is not easily fatigued and destroyed.
According to further another aspect of the present invention, there is provided a method of manufacturing a bucket tooth which is warped so that one face side becomes a concave face, comprising the steps of: heating the bucket tooth to a predetermined temperature; and causing a warp by positively applying a coolant to an almost center portion of a face on the side opposite to a side facing a bucket lip to which the bucket tooth is attached in a quenching process after the heating.
In the present invention, the bucket tooth is preferably warped by controlling the cooling speed of the coolant in the process of quenching the bucket tooth. Consequently, the desired object can be achieved by a cheap apparatus.
In the method, preferably, a surface area of a face opposite to a side facing the bucket lip is set to be larger than that of the side facing the bucket lip, and a warp is caused due to a large transformation expanding amount of the face having the larger surface area in a quenching process.
According to the present invention, the bucket tooth is warped by making a difference in surface area by setting the surface area of the surface opposite to the side facing the bucket lip to be larger than that on the side facing the bucket lip at the time of quenching the bucket tooth. Thus, the desired object can be achieved by a cheap process.
In the method, preferably, a decarburized layer on a side opposite to a side facing the bucket lip is removed and, after that, a quenching process is performed, thereby shrinking the decarburized layer to cause a warp. Specifically, a steel product is heated to 1100xc2x0 C. and subjected to blooming milling. After that, the side opposite to the side facing the bucket lip is machined to remove the decarburized layer. In such a manner, the decarburized layer is provided on the side facing the bucket lip and no decarburized layer is provided on the face on the opposite side, thereby warping the bucket tooth by using the shrinkage of the decarburized layer at the time of quenching. The tooth itself expands at the time of martensitic transformation but only the decarburized layer is shrunk. Consequently, the face having the decarburized layer becomes a concave face.
In the method of the present invention, preferably, a load may be applied to an almost center portion of a side facing the bucket lip to which said bucket tooth is attached to thereby preliminarily cause a warp after the heating and before a quenching process. As described above, both of the heat treatment method by controlling the coolant and the mechanical method can be also used to warp the bucket tooth.